Controlling X-ray imaging based on target motion

ABSTRACT

An image guided treatment is performed to treat a target. To perform the image guided treatment, measurement data indicative of target motion is acquired. A timing of one or more x-ray images is determined based on the measurement data. Treatment may be performed on the target using the position of the target.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/096,722 filed Sep. 12, 2008, and entitled,“Controlling Timing For X-Ray Imaging Based On Target Movement”, whichis hereby incorporated by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention relate to the field of image guidedtreatment and, in particular, to a system for determining a timing ofdiagnostic x-ray images based on measurement data indicative of targetmotion.

BACKGROUND

Radiosurgery and radiotherapy systems are radiation treatment systemsthat use external radiation beams to treat pathological anatomies (e.g.,tumors, lesions, vascular malformations, nerve disorders, etc.) bydelivering a prescribed dose of radiation (e.g., x-rays) to thepathological anatomy while minimizing radiation exposure to surroundingtissue and critical anatomical structures (e.g., the spinal cord). Bothradiosurgery and radiotherapy are designed to necrotize the pathologicalanatomy while sparing healthy tissue and the critical structures.Radiotherapy is characterized by a low radiation dose per treatment, andmany treatments (e.g., 30 to 45 days of treatment). Radiosurgery ischaracterized by a relatively high radiation dose in one, or at most afew, treatments.

In both radiotherapy and radiosurgery, the radiation dose is deliveredto the site of the pathological anatomy from multiple angles. As theangle of each radiation beam is different, each beam can intersect atarget region occupied by the pathological anatomy, while passingthrough different regions of healthy tissue on its way to and from thetarget region. As a result, the cumulative radiation dose in the targetregion is high and the average radiation dose to healthy tissue andcritical structures is low. Radiotherapy and radiosurgery treatmentsystems can be classified as frame-based or image-guided.

One challenge facing the delivery of radiation to treat pathologicalanatomies, such as tumors or lesions, is identifying the location of thetarget (i.e. tumor location within a patient). The most common techniquecurrently used to identify and target a tumor location for treatmentinvolves a diagnostic x-ray or fluoroscopy system to image the patient'sbody to detect the position of the tumor. This technique assumes thatthe tumor does not move appreciably over the course of a treatment.

Current methods track and account for tumor motion during delivery ofradiation treatment using multiple diagnostic x-rays over the course oftreatment, as the skilled artisan will appreciate. In these currentmethods and systems a user specifies how many radiation treatment beamsshould be delivered between each diagnostic x-ray image. In suchsystems, delivery of beams can vary drastically in time duration. Forexample, imaging every 3 beams could result in one pair of images taken10 seconds apart, interleaved by 3 short beams, followed by an imagetaken more than a minute later after 3 long beams. However, the tumormay have moved between the two diagnostic x-ray images, therebyresulting in less than desired accuracy of delivery of treatmentradiation beams to the target, and a larger than desired radiation dosedelivered to healthy tissue surrounding the target.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1 illustrates graphs showing example prostate movement during aradiation treatment session.

FIG. 2 illustrates a configuration of an image-guided radiationtreatment system, in accordance with one embodiment of the presentinvention.

FIG. 3 illustrates a configuration of an image-guided radiationtreatment system, in accordance with another embodiment of the presentinvention.

FIG. 4 illustrates a method of developing a radiation treatment plan, inaccordance with one embodiment of the present invention.

FIGS. 5A-5C illustrate timing diagrams showing a portion of an exampletreatment plan, in accordance with one embodiment of the presentinvention.

FIG. 6 illustrates one embodiment for a method of controlling the timingfor x-ray imaging.

FIG. 7A illustrates another embodiment for a method of controlling thetiming for x-ray imaging.

FIG. 7B illustrates yet another embodiment for a method of controllingx-ray imaging.

FIG. 8 illustrates one embodiment for a method of monitoring patientradiation exposure.

FIG. 9 illustrates one embodiment of systems that may be used in imageguided treatment in which features of the present invention may beimplemented.

DETAILED DESCRIPTION

Described herein is a method and apparatus for providing image guidancefor patient treatment. The following description sets forth numerousspecific details such as examples of specific systems, components,methods, and so forth, in order to provide an understanding of severalembodiments of the present invention. It will be apparent to one skilledin the art, however, that at least some embodiments of the presentinvention may be practiced without these specific details. In otherinstances, well-known components or methods are not described in detailor are presented in simple block diagram format in order to avoidunnecessarily obscuring the present invention. Thus, the specificdetails set forth are merely exemplary. Particular implementations mayvary from these exemplary details and still be contemplated to be withinthe spirit and scope of the present invention.

The term “x-ray image” as used herein may mean a visible x-ray image(e.g., displayed on a video screen) or a digital representation of anx-ray image (e.g., a file corresponding to the pixel output of an x-raydetector). Reference to an “x-ray image” may refer to a single image ora simultaneous or consecutive set of images (as in a stereoscopicimaging system). Reference to an “x-ray image” may also refer to x-rayimaging modalities such as computed tomography (e.g., cone beam CT). Theterm radiation treatment, as used herein, is the delivery of aprescribed dose of radiation to a pathological anatomy (target) of apatient. Radiation treatment includes radiosurgery (delivery of a fewrelatively high dose radiation treatments) and radiotherapy (delivery ofnumerous low dose radiation treatments).

In radiation treatment, often an entire dose of radiation that is to bedelivered to a target is not delivered in a single treatment session. Tomaximize the effect of radiation on cancer, and minimize the effect onhealthy tissue, fractionation may be used. Fractionation is a method ofradiation treatment in which the total dose of radiation to be deliveredto the target is divided into several smaller doses over a period of oneor more days. Each individual dose is referred to as a fraction.

Unless stated otherwise as apparent from the following discussion, itwill be appreciated that terms such as “processing,” “computing,”“generating,” “comparing” “determining,” “setting,” “adjusting” or thelike may refer to the actions and processes of a computer system, orsimilar electronic computing device, that manipulates and transformsdata represented as physical (e.g., electronic) quantities within thecomputer system's registers and memories into other data similarlyrepresented as physical within the computer system memories or registersor other such information storage, transmission or display devices.Embodiments of the methods described herein may be implemented usingcomputer software. If written in a programming language conforming to arecognized standard, sequences of instructions designed to implement themethods can be compiled for execution on a variety of hardware platformsand for interface to a variety of operating systems. In addition,embodiments of the present invention are not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement embodiments ofthe present invention.

One clinical area in which it is important to accurately track theposition of a target is radiotherapy or radiosurgery of the prostate totreat prostate cancer. An average patient will experience minimalprostate movement during a radiation treatment session. However,significant prostate motion happens frequently in some patients.Additionally, nearly all patients, in conventional fractionation,experience significant prostate motion in at least some of theirfractions. Moderate to significant prostate motion is experienced inabout 15% of fractions over the patient population.

FIG. 1 illustrates graphs 100 showing example prostate movement during aradiation treatment session. The graphs 100 include four separate plotsthat have time along the horizontal axis and prostate position (based ona fiducial center of mass) along the vertical axis. Each plot showsprostate motion in three different directions (superior-inferior, SI;left-right, LR; and anterior-posterior, AP), and a total combinedprostate motion (Length).

The upper left plot shows a fraction with minimal prostate motion, whichis typical in a majority of fractions (approximately 85%). For thesefractions, a diagnostic x-ray imaging frequency of approximately every1-2 minutes may be sufficient to provide sub-millimeter tracking of theprostate.

The upper right, lower right and lower left plots show typical prostatemotion for approximately 15% of fractions. The upper right plot shows acontinuous drift of the prostate, which may reflect muscles relaxingand/or a bladder filling during a single fraction. For a relativelyslow, steady prostate motion (as illustrated in the upper right plot),an imaging frequency of approximately a diagnostic x-ray image every30-60 seconds may be sufficient to provide sub-millimeter tracking ofthe prostate.

The lower right and lower left plots show irregular movement andhigh-frequency excursions, respectively, that may be a result of, forexample, rectal gas. For such rapid prostate motion, it may be necessaryto acquire diagnostic x-ray images at a diagnostic imaging frequency ofapproximately every 15-30 seconds to track the prostate motion withsub-millimeter tracking of the prostate.

Because the prostate is surrounded by radiosensitive structures (e.g.,bladder and rectum) susceptible to developing radiation toxicity, it isimportant to accurately track prostate motion throughout treatment toensure that a radiation treatment beam is not inadvertently beingdelivered to areas other than the prostate, and to ensure that adequatedoses of radiation are delivered to the prostate. As described above,the imaging frequency that is required to accurately track prostatemotion during treatment for different patients can vary dramatically.Moreover, a single patient may show minimal prostate movement during onetreatment session, and significant prostate movement during a subsequenttreatment session. A patient may also exhibit minimal prostate motionfor some of a treatment session, and exhibit significant prostate motionfor the remainder of the treatment session. Therefore, it can beimportant to provide a mechanism both to set the imaging frequencybefore radiation treatment, and to adjust the imaging frequency duringradiation treatment. The general concept is to image as frequently asnecessary to track the target accurately (e.g. within a tolerance of 1mm), but not necessarily as frequently as is possible, because it isdesirable to minimize ionizing radiation delivered from the diagnosticimaging. This can be especially important for treatments such ashypofractionated prostrate radiosurgery (radiation therapy that giveslarger doses, e.g., up to 14 Gy per fraction, in a reduced number oftreatment sessions) for at least two reasons: high dose and reducednumber of fractions.

Note that radiation treatment of the prostate is described herein forpurpose of example. Embodiments of the present invention may equallyapply to a broad spectrum of patient anatomies (e.g., organs) within thebody that can move. For example, embodiments of the present inventionmay be applied to treatment of the liver or pancreas, or any otherinternal target.

FIGS. 2 and 3 illustrate configurations of image-guided radiationtreatment systems 200 and 300, in accordance with embodiments of thepresent invention. In the illustrated embodiments, the radiationtreatment systems 200 and 300 include a linear accelerator (LINAC) 201that acts as a radiation treatment source. The LINAC 201 is mounted onthe end of a robotic arm 202 having multiple (e.g., 5 or more) degreesof freedom in order to position the LINAC 201 to irradiate apathological anatomy (e.g., target 220) with beams delivered from manyangles, in many planes, in an operating volume around a patient.Treatment may involve beam paths with a single isocenter, multipleisocenters, or with a non-isocentric approach. Alternatively, the LINAC201 may be mounted on a gantry to provide isocentric beam paths.

The LINAC 201 may be positioned at multiple different nodes (predefinedpositions at which the robot stops and radiation may be delivered)during treatment by moving the robotic arm 202. At the nodes, the LINAC201 can deliver one or more radiation treatment beams to a target. Thenodes may be arranged in an approximately spherical distribution about apatient. The particular number of nodes and the number of treatmentbeams applied at each node may vary as a function of the location andtype of pathological anatomy to be treated. For example, the number ofnodes may vary from 50 to 300, or more preferably 15 to 100 nodes andthe number of beams may vary from 200 to 3200, or more preferably 50 to300.

Referring to FIG. 2, radiation treatment system 200, in accordance withone embodiment of the present invention, includes an imaging system 210having a processor 230 connected with x-ray sources 203A and 203B andfixed x-ray detectors (imagers) 204A and 204B. Alternatively, the x-raysources 203A, 203B and/or x-ray detectors 204A, 204B may be mobile, inwhich case they may be repositioned to maintain alignment with thetarget 220, or alternatively to image the target from differentorientations or to acquire many x-ray images and reconstruct athree-dimensional (3D) cone-beam CT. In one embodiment the x-ray sourcesare not point sources, but rather x-ray source arrays, as would beappreciated by the skilled artisan. In one embodiment, LINAC 201 servesas an imaging source (whether gantry or robot mounted), where the LINACpower level is reduced to acceptable levels for imaging.

Imaging system 210 may perform computed tomography (CT) such as conebeam CT, and images generated by imaging system 201 may betwo-dimensional (2D) or three-dimensional (3D). The two x-ray sources203A and 203B may be mounted in fixed positions on the ceiling of anoperating room and may be aligned to project x-ray imaging beams fromtwo different angular positions (e.g., separated by 90 degrees) tointersect at a machine isocenter (which provides a reference point forpositioning the patient on a treatment couch 206 during treatment) andto illuminate imaging planes of respective detectors 204A and 204B afterpassing through the patient. Imaging system 210, thus, providesstereoscopic imaging of the target 220 and the surrounding volume ofinterest (VOI). In other embodiments, imaging system 210 may includemore or less than two x-ray sources and more or less than two detectors,and any of the detectors may be movable rather than fixed. In yet otherembodiments, the positions of the x-ray sources and the detectors may beinterchanged. Detectors 204A and 204B may be fabricated from ascintillating material that converts the x-rays to visible light (e.g.,amorphous silicon), and an array of CMOS (complementary metal oxidesilicon) or CCD (charge-coupled device) imaging cells that convert thelight to a digital image that can be compared with a reference imageduring an image registration process that transforms a coordinate systemof the digital image to a coordinate system of the reference image, asis well known to the skilled artisan. The reference image may be, forexample, a digitally reconstructed radiograph (DRR), which is a virtualx-ray image that is generated from a 3D CT image based on simulating thex-ray image formation process by casting rays through the CT image.

Imaging system 210 can generate diagnostic x-ray images at a pre-definedimaging frequency for updating a current location of the target. Eachdiagnostic x-ray image may be compared to the reference image (e.g.,corresponding DRR) and/or to previous diagnostic x-ray images todetermine present target location and a rate of target movement. Iftarget movement is higher than a predefined tolerance (e.g., 1 mm/min.),the imaging system may increase the imaging frequency to update targetlocation and more accurately direct radiation to the moving target. Iftarget movement is lower than the predefined tolerance, the imagingsystem 210 may decrease the imaging frequency, as fewer images arenecessary to track target movement within the desired tolerances. Itwill be appreciated that upper and lower predefined tolerances may beselected, thereby defining a range of movement where the imagingfrequency is satisfactory, and where the frequency is increased ordecreased if movement is above or below (respectively) the upper andlower predefined tolerances. Changing the imaging frequency in responseto target movement is discussed in greater detail below with referenceto FIGS. 7A and 7B.

Referring to FIG. 3, in alternative embodiments an imaging system 310includes a motion detection device 312 to determine target motion, themotion detecting device 312 having a detection field 340. If the motiondetecting device 312 detects motion that exceeds a treatment tolerance,x-ray imaging device 313 may be directed to generate a new diagnosticx-ray image at a region within an imaging field 350. The motiondetecting device 312 can be any sensor or other device capable ofidentifying target movement. The motion detecting device 312, may be,for example an ultrasound scanner, an optical sensor such as a camera, apressure sensor, an electromagnetic sensor, or some other sensor thatcan provide motion detection without delivering ionizing radiation to auser (e.g., a sensor other than an x-ray imaging system). In oneembodiment, the motion detecting device 312 acquires measurement dataindicative of target motion in real-time. Alternatively, the measurementdata may be acquired at a frequency that is higher (potentiallysubstantially higher) than can be achieved or than is desirable withx-ray imaging (due to ionizing radiation delivered to the patient witheach x-ray image). In one embodiment, the motion detecting device 312does not provide a high absolute position accuracy. Instead, the motiondetecting device 312 may provide sufficient relative position accuracyto detect patient movement and/or target movement. Such motion detectionmay trigger the acquisition of an image having high position accuracy(e.g., an x-ray image).

In one embodiment, the motion detecting device 312 is an ultrasoundscanner. The ultrasound scanner may include a one-dimensional (1D) arrayof transducer elements that produces two-dimensional (2D) ultrasoundimages, or that is mechanically rotated to produce a series of 2D imagesthat are compounded into a 3D image, or a 2D array of transducerelements that produces 3D images. While patient 225 is lying ontreatment couch 206, a transducer of the ultrasound scanner may be heldin place on the skin surface of patient 225 (or alternatively placed inthe rectum, i.e., transrectal ultrasound). The location of the target220 may be determined as a positional offset between the target 220 andthe transducer of the ultrasound scanner. In one embodiment, atransducer or transducers of the ultrasound scanner can be tracked suchthat detected motion is in the treatment room coordinate system.

In another embodiment, the motion detecting device 312 is an opticalsystem, such as a camera. The optical system may track the position oflight-emitting diodes (LEDs) situated on patient 225. Alternatively, theoptical system may directly track a surface region of patient 225, asdistinguished from tracking LEDs on the patient. There may be acorrelation between movement of the target and movement of the LEDsand/or surface region of the patient 225. Based on the correlation, whenmotion of the LEDs and/or surface region is detected, it can bedetermined that the target 220 has also moved sufficiently to requireanother diagnostic x-ray image to precisely determine the location ofthe target.

In another embodiment, the motion detecting device 312 includes a radiofrequency identification (RFID) system having an interrogator thattracks a location of a transponder located on or in patient 225 based ontime of flight of a radio frequency (RF) signal. Alternatively, motiondetecting device 312 may be some other type of device that is capable oflocating a target, such as an electromagnetic coil array or a laserrange finder. Other examples of motion detecting devices 312 includestrain gauges, piezoelectric sensors, respirometers, etc.

Before a patient undergoes radiation treatment, a radiation treatmentplan is typically developed. A radiation treatment plan is a plan forthe delivery of radiation treatment beams to the pathological anatomy ofthe patient from a number of treatment nodes, with one or more beams(having one or more shapes, angles or orientations) being applied fromeach node. A radiation treatment plan may also call for acquisition of anumber and/or timing of intra-treatment diagnostic x-ray images, whichare used to track the location of the target; diagnostic x-ray imagesare one example of intra-treatment data collected to track the positionof the target. For example, and without limitation, diagnostic x-rayimages are registered (as known by the skilled artisan) withpre-treatment 3D image data (e.g., CT image, cone-beam CT image, or MRimage). Moreover, a radiation treatment plan may include an imagingprotocol that identifies, for example, an imaging modality to use (e.g.,single x-ray projections, multiple x-ray projections, etc), an imagingalgorithm or algorithms to use, whether to track fiducials or patientanatomy, etc.

As noted, the diagnostic image data are used to track the location ofthe pathological anatomy during the course of delivering radiationthereto. The location of the pathological anatomy is well knownimmediately after diagnostic image data is obtained and analyzed. Astime passes following acquisition and analysis of the diagnostic imagedata, the location of the pathological anatomy becomes less certain. Thepathological anatomy may remain relatively stationary, it may moveslightly or it may have dramatic movements, such as the prostate examplepreviously described. The movements can be caused for any of a number ofreasons including, without limitation, patient movement, naturalshifting due to non-rigidness of the anatomy, or movement of an adjacentpiece of anatomy (e.g., bladder filling, rectal gas etc.). In any event,less certainty in the location of the pathological anatomy results inless certainty that the radiation delivered based on the last diagnosticimage data is being delivered as planned with the desired accuracy. Theamount of time from diagnostic image data acquisition and analysis tothe approximate time after completing the delivery of the latesttreatment beam is defined as the image age. To better understand imageage within the context of this description, one may consider an imageage of zero as that time where the system has the most up to date dataon target location. As the image age increases, the target location dataages, and may become less reliable depending on how fast the target ismoving or how much the target has moved during that time period. In oneembodiment, a radiation treatment plan includes an image age thresholdthat specifies the maximum allowable image age (e.g., at the end of beamdelivery) for a diagnostic x-ray image.

FIG. 4 illustrates a method 400 of developing a radiation treatmentplan, in accordance with one embodiment of the present invention. Method400 may also adjust a preexisting radiation treatment plan during thetreatment. For example, if a clinician selects an image age threshold(maximum allowable image age) before treatment begins or duringtreatment, method 400 may adjust a preexisting radiation treatment planbased on the image age threshold. In one embodiment, method 400 isperformed by a radiation treatment system (e.g., radiation treatmentsystem 200 or 300). Alternatively, method 400 may be performed by atreatment planning system, or by other types of image guided treatmentsystems.

At block 405, a treatment planning system (or treatment delivery system)determines multiple radiation treatment beams to be delivered to atarget (e.g., a pathological anatomy of a patient). Each radiationtreatment beam may be delivered from one of many possible nodes.Moreover, each radiation treatment beam may be delivered from aparticular orientation at a selected node. For example, a radiationtreatment beam may be delivered by a LINAC 201 that is oriented suchthat it is not aiming at the isocenter.

At block 410, a selection of an image age threshold (maximum allowableimage age) is received. Selection of the image age threshold may bereceived from a clinician, or calculated based on predicted targetmovement. The selected image age threshold may be based on an expectedamount of target movement, based for example on a statisticallysignificant historical sample of patients undergoing the same or similarprocedure. For example, a prostate may move a clinically insignificantamount over a period of 10 seconds. Therefore, a maximum image age of 10seconds may be selected to ensure that movement of the patient/targetwill not result in unwanted radiation beam delivery to healthy tissuesurrounding the prostate. An x-ray imaging frequency and x-ray imagingperiod may be calculated based on the image age threshold. For example,if the image age threshold is 10 seconds, the calculated x-ray imagingperiod may be 10 seconds or less. The x-ray imaging frequency dictatesthe minimum frequency at which diagnostic x-ray images will be taken.The x-ray imaging period dictates the maximum length of time betweensequential diagnostic x-ray images, and is the reciprocal of the x-rayimaging frequency. In a further embodiment, the image age thresholddefines the x-ray imaging frequency and the x-ray imaging period.

In one embodiment, the imaging system has an inherent maximumsustainable imaging frequency that cannot be exceeded. In a furtherembodiment, if a diagnostic x-ray image is to be taken at a frequencythat is greater than the maximum sustainable imaging frequency, then adelay is introduced so that the maximum sustainable imaging frequencyrequirement is satisfied. For example, if the maximum sustainableimaging frequency indicates that the diagnostic x-ray images cannot betaken more frequently than every 5 seconds, and a new diagnostic x-rayimage is to be taken 2 seconds after a previous x-ray, the new x-ray andtreatment may be delayed such that it is taken 5 seconds after theprevious x-ray. This may prevent damage to the imaging system.

At block 412, the treatment planning system (or a treatment deliverysystem) schedules a diagnostic x-ray image to be generated. Duringtreatment, the diagnostic x-ray image may be compared to a previouslygenerated image, such as a DRR or a previous diagnostic x-ray image, todetermine a target location before delivering radiation treatment beams.At block 415, the treatment planning system (or the treatment deliverysystem) determines whether completion of the next radiation treatmentbeam exceeds the image age threshold, in which case the method proceedsto block 420.

At block 420, the radiation treatment beam is divided into multipleradiation treatment beams. Each of the multiple radiation treatmentbeams can have an equivalent power level, node position and orientationas the original radiation treatment beam, but have a shorter durationsuch that each of the multiple treatment beams can be completed withinan image age threshold. In one embodiment, the duration of each of themultiple radiation treatment beams is less than the image age threshold.Alternatively, durations of the multiple radiation treatment beams canbe selected such that on average the radiation treatment beams areapproximately less than or equal to the image age threshold. In such anembodiment, a maximum radiation treatment beam duration may be set suchthat no radiation treatment beam is longer than the image age thresholdby, for example, 20% of the length of the image age threshold. Radiationtreatment beams may then have durations of up to 120% of the image agethreshold. Radiation treatment beams that would not be completed before120% of the image age threshold would, therefore, be preceded by adiagnostic x-ray image to ensure a sufficiently low image age, and,therefore, sufficiently high confidence of target location prior todelivery of radiation. Accordingly, a diagnostic x-ray image will notbecome too old upon which to rely for target location information beforedelivery of radiation treatment beams.

At block 425, the system determines whether the amount of time that haselapsed since a last diagnostic x-ray image was taken will exceed theimage age threshold before a next treatment beam is completed, in whichcase then a diagnostic x-ray image may become too old to rely upon fordetermination of a location of the target before delivery of the nextradiation treatment beam. If delivery of a treatment beam extends beyondthe image age threshold, the target may move beyond a tolerated amountduring delivery of the radiation treatment beam, and a portion of theradiation treatment beam may be unintentionally delivered to healthytissue. If the image age threshold will be exceeded before the nexttreatment beam is completed, the method proceeds to block 430.Otherwise, the method proceeds to block 435. At block 430, a diagnosticx-ray image is scheduled to be taken before beginning delivery of thenext radiation treatment beam. The method then proceeds to block 435. Inone embodiment, the duration of the radiation treatment beam includestime that elapses before the treatment beam is actually delivered due topreparation of the treatment beam. Such time is referred to herein astargeting correction overhead, and includes the time that it takes toposition the LINAC into a predetermined position and/or orientation(e.g., due to LINAC reposition between nodes and/or within nodes).

At block 435, the treatment planning system (or treatment deliverysystem) determines whether there are any additional radiation treatmentbeams included in the treatment plan. If there are additional radiationtreatment beams, the method returns to block 415, and the next radiationtreatment beam is compared to the image age threshold. Otherwise, themethod ends, and the treatment plan may be completed.

Treatment plans may be modified according to method 400 withoutsignificantly increasing the duration of patient treatment. Moreover,the final number of diagnostic x-ray images taken of a patient may notbe significantly increased over other imaging methodologies (e.g., ascompared to a methodology in which a set number of treatment beams aredelivered between each diagnostic x-ray image). Consequently, overallradiation exposure to a patient may not increase significantly as aresult of implementing method 400, but treatment delivery accuracy isincreased. Radiation exposure due to x-ray imaging is discussed ingreater detail below with reference to FIG. 8.

FIGS. 5A-5C illustrate timing diagrams showing a portion of an exampletreatment plan, in accordance with one embodiment of the presentinvention. In FIG. 5A, the example treatment plan 500 has not beenadjusted by method 400. Treatment plan 500 calls for a diagnostic x-rayimage 502 that takes 3 seconds to acquire, followed by LINAC reposition504 (e.g., motion of the robotic arm that aims a LINAC) that takes 1second. After the LINAC reposition, a first treatment beam 506 isscheduled to be delivered for 12 seconds, followed by LINAC reposition508 for another 1 second. A second treatment beam 510 is then to bedelivered for six seconds.

FIG. 5B illustrates an example treatment plan 520 corresponding toexample treatment plan 500 after it has been adjusted by method 400based on an image age threshold of 10 seconds, in accordance with oneembodiment of the present invention. As shown, the first diagnosticx-ray image 502 and LINAC reposition 504 are unchanged. However, thefirst treatment beam 506 had a duration that exceeded the image agethreshold, and was split into treatment beam 1A 526 and treatment beam1B 534. Treatment beam 1A 526, having a duration of 6 seconds, isscheduled to be delivered after a first diagnostic x-ray image 502 istaken. If delivery of treatment beam 1B 534 took place immediately aftercompleting delivery of treatment beam 1A 526, then completing deliveryof treatment beam 1B 534 would exceed the image age threshold.Therefore, a second diagnostic x-ray image 530 is scheduled to be takenbefore delivery of treatment beam 1B 534. A third diagnostic x-ray image538 is scheduled to be taken before delivery of second treatment beam510 is scheduled to be delivered.

Before the second diagnostic x-ray image 530 and the third diagnosticx-ray image 538 are taken, additional LINAC repositions 528 and 536 areindicated to reposition the LINAC to aim at a treatment isocenter. SuchLINAC repositions 528, 536 are a precaution to ensure that the LINACdoes not interfere with (e.g., block a portion of) the diagnostic x-rayimage. In one embodiment, it may be known which LINAC positions willinterfere with x-ray imaging, and motion of the robot may be planned inconjunction with the acquisition of new diagnostic x-ray images toreduce overall treatment time. The skilled artisan will appreciate thatall time and time durations provided herein are by way of explanationand not limitation. Longer or shorter times or time durations may beused without exceeding the scope of the present teachings.

FIG. 5C illustrates an example treatment plan 540 corresponding toexample treatment plan 500 after it has been adjusted by method 400based on an image age threshold of 10 seconds, in accordance withanother embodiment of the present invention. In FIG. 5C, the firsttreatment beam 506 has been separated into treatment beam 1A 546, havinga duration of 10 seconds, and treatment beam 1B 554, having a durationof 2 seconds. After treatment beam 1A 546 is delivered, a seconddiagnostic x-ray image 550 is taken. However, unlike the example shownin FIG. 5B, in FIG. 5C both treatment beam 1B 554 and second treatmentbeam 510 can be delivered before 10 seconds have passed from the time ofthe second diagnostic x-ray 550. As shown in FIG. 5C, the treatmentplanning system may divide treatment beams in such a way so as tominimize the number of diagnostic x-ray images needed, which can reduceoverall x-ray exposure to a patient.

FIG. 6 illustrates one embodiment for a method 600 of controlling thetiming for x-ray imaging. In one embodiment, method 600 is performed byradiation treatment system 200 of FIG. 2 or radiation treatment system300 of FIG. 3. At block 605, a radiation treatment plan that includespredicted target movement, multiple radiation treatment beams, and aninitial x-ray imaging frequency/period is received. The initial x-rayimaging frequency/period may be based on an image age threshold. In oneembodiment, the x-ray imaging frequency and x-ray imaging period reflecta target x-ray imaging frequency and target x-ray imaging period basedon the image age threshold. The actual timing of some diagnostic x-rayimages may cause those diagnostic x-ray images to be taken sooner thanthe x-ray imaging period or later than the x-ray imaging period.Therefore, the actual timing of diagnostic x-ray images may average tothe initial x-ray imaging frequency/period. For examples of how atreatment beam may be divided, and when diagnostic x-ray images may bescheduled refer back to FIGS. 5A-5C.

Image guided radiation treatment may be initiated using the receivedtreatment plan. At block 610, a diagnostic x-ray image of the target isacquired. The diagnostic x-ray image may be used to compute a locationof the target so as to accurately deliver radiation treatment beams tothe target, preferably while avoiding delivering radiation treatmentbeams to nearby sensitive structures. One or more radiation treatmentbeams may be delivered subsequent to acquiring the x-ray image of thetarget.

If the age of the x-ray image will exceed an image age threshold, thenan additional diagnostic x-ray image may be acquired prior to deliveringany more radiation treatment beams. This can ensure that radiationtreatment beams are precise and accurate. At block 615, an additionalx-ray image is acquired of the target. At block 620, the imaging systemcompares the first diagnostic x-ray image to the additional diagnosticx-ray images to track target movement. Differences between thesequential images may be used to register a patient coordinate systemwith a treatment coordinate system to ensure that the treatment beamsare accurately positioned with respect to the pathological anatomy.Differences between the sequential images may be measured using methodsknown in the art such as feature recognition, pattern intensitymatching, etc.

At block 625, it is determined whether the target movement is within atreatment tolerance that is based on a predicted target movement. Forexample, a certain amount of target movement may be expected andaccounted for by the treatment plan. However, if the differences betweensequential diagnostic x-ray images indicate an amount of target movementthat is different from the expected or planned amount of movement, itmay be necessary to adjust the x-ray imaging frequency to better targetthe radiation beams. Accordingly, if target movement is not within thetreatment tolerance (e.g., if the target movement indicated by thedifferences between the sequential diagnostic x-ray images is greaterthan the planned or expected target movement during the time interval),the method may proceed to block 630, and the x-ray imaging frequency maybe increased (the image age threshold may also be decreased). Forexample, it may be expected that a patient's prostate will move at arate of 1 mm per minute, and the x-ray imaging frequency may beinitially set such that the prostate will not move more than 1 mmbetween sequential diagnostic x-ray images. However, if the prostate isdetected to have moved more than 1 mm between sequential diagnosticx-ray images, then the x-ray imaging frequency may be increased toensure that the prostate does not move more than 1 mm between subsequentdiagnostic x-ray images. If the time intervals between subsequentdiagnostic x-ray images have been decreased, then the total number ofdiagnostic x-ray images may be increased in response to greater thanexpected target movement.

In one embodiment, if the target movement is approximately equal to thepredicted target movement, then the method proceeds to block 660. If thetarget movement is less than the predicted target movement the methodproceeds to block 635, then the x-ray imaging frequency may be decreased(the image age threshold may also be increased), after which the methodproceeds to block 645. If the time intervals between subsequentdiagnostic x-ray images have been increased in response to less thanexpected target movement, then the total number of x-ray images may bedecreased.

At block 645, it is determined whether any radiation treatment beamshaving the same node and orientation can be combined and still completedelivery within the x-ray imaging period (which may be based on theimage age threshold). For example, a treatment plan may identify that aparticular dose of radiation is to be delivered to the target from aspecified position and orientation of the LINAC. Due to the initialx-ray imaging frequency/period, that dose of radiation may be deliveredin multiple treatment beams, so that no treatment beam is beingdelivered to the patient after the image age threshold. Once the x-rayimaging frequency has been decreased, some of these multiple treatmentbeams may be combined, and still satisfy the image age threshold. Toprovide an illustration, if the image age threshold were adjusted to 12seconds in the example described with reference to FIGS. 5A-5C, then thetreatment plans 520 and 540 could be revised to resemble treatment plan500. If treatment beams can be combined the method proceeds to block655, otherwise the method proceeds to block 660.

At block 640, it is determined whether any radiation treatment beam willcomplete delivery outside of the x-ray imaging period (extends beyondthe image age threshold). If a radiation treatment beam will notcomplete delivery within the x-ray imaging period, the method proceedsto block 650. Otherwise the method proceeds to block 660.

At block 650, any radiation treatment beam that will complete deliveryoutside of the x-ray imaging period (extend beyond the image agethreshold) is divided into multiple radiation treatment beams. Forexample, if a radiation treatment beam has a duration that is greaterthan the x-ray imaging period, it may be divided.

At block 660, the imaging system computes a target location based on thex-ray image or the additional x-ray image. At block 665, the treatmentsystem directs radiation treatment beams using the target location.

At block 670, it is determined whether the treatment has been completed.If the treatment is not yet complete, the method continues to block 675.If the treatment is complete, the method ends.

At block 675, the treatment system determines whether the age of thediagnostic x-ray image will exceed the image age threshold before thetime to completion. If the diagnostic x-ray image age will exceed theimage age threshold before the time to completion, the method proceedsto block 615, and a new diagnostic x-ray image may be obtained.Otherwise the method proceeds to block 665, and another radiationtreatment beam is delivered to the patient.

In one embodiment, rather than computing target movement based onsequential x-ray images, in method 600 target movement may instead beinferred based on detected patient motion. Such patient motion may bedetected by an optical scanner that collects image data, a laser rangefinder, an RFID system, etc. Alternatively, the motion detecting devicemay measure target motion directly, but may not have a resolution thatis high enough to accurately identify the target location for purposesof delivering a radiation treatment beam. For example, the motiondetecting device may be an ultrasonic imager that takes ultrasonicimages of the target. In such embodiments, at block 615 data other thanan x-ray image that is indicative of target motion may be acquiredinstead of, or in addition to, the x-ray image. In such an embodiment,Block 620 may be skipped, and the data indicative of target motion maybe used to determine an amount of target motion.

FIG. 7A illustrates another embodiment for a method 700 of controllingthe timing for x-ray imaging. Method 700 may control the timing of asingle diagnostic x-ray image or of multiple diagnostic x-ray imagestaken at different times. Where the timing of multiple diagnostic x-rayimages is controlled, such control may include controlling an x-rayimaging frequency (and an x-ray imaging period). In one embodiment,method 700 is performed by radiation treatment system 300 or radiationtreatment system 200.

At block 705, a diagnostic x-ray image is acquired of a target. At block710, measurement data indicative of target movement (e.g., a diagnosticx-ray, ultrasound sensor readings, camera readings, etc.) is acquired.The measurement data may be acquired by monitoring the patient with amotion detecting device 313 as described with reference to FIG. 3.Alternatively, the measurement data may be acquired by an imaging systemthat uses comparisons of sequential diagnostic x-ray images and/or acomparison of current diagnostic x-ray images with pretreatment imagesto determine whether larger than expected target movement has occurred.

At block 715, target movement is analyzed, and compared to a movementthreshold, which may be user selected or predetermined. The targetmovement may result from a sudden patient movement, such as those due tomuscle twitches, spasms (e.g., a cough, sneeze, shudder, etc.),voluntary patient movement (e.g., patient shifting body), or gradualmovement (e.g., bladder filling or muscles relaxing). Suchpatient/target movement may cause enough movement in the target to makethe radiation treatment beam to miss the target and hit surroundinghealthy tissues and critical structures. If target movement exceeds amovement threshold, then the method proceeds to block 720, and anadditional diagnostic x-ray image of the target is acquired. Moreover,if an x-ray imaging frequency is used to control the timing of x-rayimaging, the x-ray imaging frequency may be modified to account for theincreased target motion. If the target movement is within the targetthreshold, the method proceeds to block 725, where the imaging systemcomputes a target position based on the diagnostic x-ray image and/orthe additional diagnostic x-ray image. At block 730, a treatment systemperforms image guided treatment using the target position.

FIG. 7B illustrates yet another embodiment for a method 750 ofcontrolling x-ray imaging. Method 750 may control the timing of a singlediagnostic x-ray image or of multiple diagnostic x-ray images taken atdifferent times. Where the timing of multiple diagnostic x-ray images iscontrolled, such control may include controlling an x-ray imagingfrequency (and an x-ray imaging period). In one embodiment, method 750is performed by radiation treatment system 300 or radiation treatmentsystem 200.

At block 755, a diagnostic x-ray image is acquired of a target. Thex-ray image can be one or more 2D projection x-ray images, a 3D CTimage, etc. of the target. At block 760, a position of the target iscomputed based on the x-ray image. The computed position can be used toaccurately determine where to place a radiation treatment beam. At block765, radiation treatment is begun or resumed based on the computedposition of the target.

At block 770, measurement data indicative of target movement isacquired. While treatment is in progress, measurement data indicative oftarget movement may be continually or periodically acquired. Themeasurement data may be acquired by an ultrasound sensor, an opticalsensor such as a camera, a pressure sensor, a laser range finder, anelectromagnetic sensor, or some other sensor that can provide motiondetection without delivering ionizing radiation to a user (e.g., asensor other than an x-ray imaging system). In one embodiment, themeasurement data is acquired in real-time by the sensor. Alternatively,the measurement data may be acquired at a frequency that is higher(potentially substantially higher) than can be achieved or than isdesirable with x-ray imaging (due to radiation dose delivered to thepatient with each x-ray image). In one embodiment, the measurement datadoes not provide a high absolute position accuracy. Instead, themeasurement data may provide sufficient relative position accuracy todetect patient movement and/or target movement.

At block 775, the measurement data is analyzed to determine or estimatea target motion. The measurement data may be a direct measurement of thetarget motion, or may be a measurement of movement of an external orinternal landmark that is indicative of target motion. Examples ofexternal landmarks include, for example, the chest or head of thepatient. The target motion is compared to a specified motion threshold,which may be user selected or predetermined. If the target motionexceeds the motion threshold (is outside the specified treatmenttolerance), then the method proceeds to block 780. If the target motiondoes not exceed the motion threshold (is within the specified treatmenttolerance), the method proceeds to block 785.

At block 780, the radiation treatment may be paused, or a currentradiation treatment beam that is being delivered to the patient may becompleted, after which treatment is paused. The method then returns toblock 755 to acquire a new x-ray image.

At block 785, the system determines whether radiation treatment hascompleted. Radiation treatment is complete when all radiation treatmentbeams for a treatment session have been delivered to the patient. If theradiation treatment has not completed, the method proceeds to block 790,and the radiation treatment continues using the target position that wascomputed based on the last x-ray image. The method then continues toblock 770 to continue acquiring measurement data indicative of targetmotion. If the radiation treatment has completed, the method ends.

Each diagnostic x-ray image taken of a patient exposes the patient to anamount of radiation. The amount of radiation that a diagnostic x-rayimage exposes the patient to depends on the power level of the x-raysource and on the duration of a diagnostic x-ray beam used to generatethe diagnostic x-ray image. During image guided treatment, multiplediagnostic x-ray images are typically taken. Therefore, image guidedtreatment (which may include a single treatment session and/or multipletreatment sessions) may expose the patient to increased levels ofradiation. In one embodiment, the amount of radiation that is deliveredand that will be delivered to a patient is monitored. If total radiationexposure for a treatment will exceed a radiation exposure threshold, atreatment plan may be adjusted to reduce the total radiation deliveredto the patient.

FIG. 8 illustrates a method 800 of monitoring patient x-ray exposure, inaccordance with one embodiment of the present invention. Method 800 maybe performed whenever an x-ray imaging frequency or an image agethreshold is modified for a radiation treatment plan. Alternatively,method 800 may be performed periodically or continuously to ensure thata patient is not exposed to excessive radiation. In one embodiment,method 800 is performed by radiation treatment system 300 or byradiation treatment system 200.

At block 805, a current radiation treatment exposure of a patient isdetermined. The current radiation treatment exposure can be determinedbased on the number of x-rays that the patient has received, and thepower and duration of each of the x-rays (i.e., dose delivered to thepatient via x-ray imaging). Each of these values may be recorded asdiagnostic x-ray images are taken, and/or may be included in a radiationtreatment plan for the patient. At block 810, a number of expectedfuture diagnostic x-ray images are identified, and may include allx-rays images that will be delivered to the patient during treatment.Treatment may occur over a period of days or weeks, or may occur in asingle day. The number of future x-rays images may be determined byanalyzing the number of images scheduled in a radiation treatment plan.Alternatively, the number of future images may be determined based on anx-ray imaging frequency. At block 815, an amount of radiation to bedelivered by future x-ray imaging is determined, which can be calculatedbased on the power level and duration of the future x-ray images. Atblock 820, the total amount of radiation exposure for the patient isdetermined by adding the current radiation exposure and the predictedfuture radiation exposure. At block 825, the total predicted patientradiation exposure is compared to a radiation exposure threshold. If thetotal predicted radiation exposure exceeds the radiation exposurethreshold, the method proceeds to block 830. Otherwise the method ends.

At block 830, a radiation treatment plan for the patient is modified toreduce the amount of radiation to which the patient will be exposed. Anexample of a modification that can be made to reduce radiation exposureis reducing the imaging frequency to limit the number of x-rays thatwill be delivered to the patient. In one embodiment, a maximum imagingfrequency is set. If a clinician attempts to adjust an imaging frequencybeyond the maximum imaging frequency, the clinician may be warned thatthe patient may be exposed to unhealthy levels of radiation.Alternatively, it may not be possible to exceed the maximum imagingfrequency. Another example of a modification that can be made to theimage treatment plan to reduce radiation exposure is reducing the powerlevel of diagnostic x-ray images. Other adjustments can also be made, aswill be appreciated by the skilled artisan. At block 835, the predictedand current radiation exposure for the patient is displayed. The methodthen ends.

FIG. 9 illustrates one embodiment of systems that may be used inperforming radiation treatment in which features of the presentinvention may be implemented. As described below and illustrated in FIG.9, a system 900 may include a diagnostic imaging system 905, a treatmentplanning system 910, a treatment delivery system 915 and a motiondetecting system 906. In one embodiment, the diagnostic imaging system905 and the motion detecting system 906 are combined into a single unit.

Motion detecting system 906 may be any system capable of detectingpatient motion and/or target motion. For example, motion detectingsystem 906 may be a computed tomography (CT) system, an ultrasoundsystem, video camera, or the like. Motion detecting system 906 includesone or more sensors 908 for detecting patient and/or target motion. Forexample, a video camera may include a lens and array of charge coupleddevices (CCDs) for converting incident light into an electrical signal.

The sensor (or sensors) 908 may be coupled to a digital processingsystem 912 to control the motion detecting operation and process sensordata. Motion detecting system 906 includes a bus or other means 982 fortransferring data and commands among digital processing system 912 andsensor 908. Digital processing system 912 may include one or moregeneral-purpose processors (e.g., a microprocessor), special purposeprocessor such as a digital signal processor (DSP) or other type ofdevice such as a controller or field programmable gate array (FPGA).Digital processing system 912 may also include other components (notshown) such as memory, storage devices, network adapters and the like.Digital processing system 912 may compute target motion. Digitalprocessing system 912 may transmit the target motion to treatmentdelivery system 915 over a data link 984 or to diagnostic imaging system905 over data link 988, which may be, for example, direct links, localarea network (LAN) links or wide area network (WAN) links such as theInternet. In addition, the information transferred between systems mayeither be pulled or pushed across the communication medium connectingthe systems, such as in a remote diagnosis or treatment planningconfiguration.

Diagnostic imaging system 905 may be any system capable of producingmedical diagnostic images of a patient that may be used for subsequentmedical diagnosis, treatment planning and/or treatment delivery. Forexample, diagnostic imaging system 905 may be a computed tomography (CT)system, a magnetic resonance imaging (MRI) system, a positron emissiontomography (PET) system, an ultrasound system or the like. For ease ofdiscussion, diagnostic imaging system 905 may be discussed below attimes in relation to a CT x-ray imaging modality. However, other imagingmodalities such as those above may also be used.

In one embodiment, diagnostic imaging system 905 includes an imagingsource 920 to generate an imaging beam (e.g., x-rays, ultrasonic waves,radio frequency waves, etc.) and an imaging detector 930 to detect andreceive the beam generated by imaging source 920, or a secondary beam oremission stimulated by the beam from the imaging source (e.g., in an MRIor PET scan).

The imaging source 920 and the imaging detector 930 may be coupled to adigital processing system 925 to control the imaging operation andprocess image data. In one embodiment, diagnostic imaging system 905receives motion data from motion detecting system 906, and determineswhen to acquire images based on the motion data. In another embodiment,diagnostic imaging system 905 may receive imaging commands fromtreatment delivery system 915.

Diagnostic imaging system 905 includes a bus or other means 980 fortransferring data and commands among digital processing system 925,imaging source 920 and imaging detector 930. Digital processing system925 may include one or more general-purpose processors (e.g., amicroprocessor), special purpose processor such as a digital signalprocessor (DSP) or other type of device such as a controller or fieldprogrammable gate array (FPGA). Digital processing system 925 may alsoinclude other components (not shown) such as memory, storage devices,network adapters and the like. Digital processing system 925 may beconfigured to generate digital diagnostic images in a standard format,such as the DICOM (Digital Imaging and Communications in Medicine)format, for example. In other embodiments, digital processing system 925may generate other standard or non-standard digital image formats.Digital processing system 925 may transmit diagnostic image files (e.g.,the aforementioned DICOM formatted files) to treatment delivery system915 over a data link 983, which may be, for example, a direct link, alocal area network (LAN) link or a wide area network (WAN) link such asthe Internet. In addition, the information transferred between systemsmay either be pulled or pushed across the communication mediumconnecting the systems, such as in a remote diagnosis or treatmentplanning configuration. In remote diagnosis or treatment planning, auser may utilize embodiments of the present invention to diagnose ortreat a patient despite the existence of a physical separation betweenthe system user and the patient.

Treatment delivery system 915 includes a therapeutic and/or surgicalradiation source 960 to administer a prescribed radiation dose to atarget volume in conformance with a treatment plan. Treatment deliverysystem 915 may also include a digital processing system 970 to controlradiation source 960, receive and process data from diagnostic imagingsystem 905 and/or motion detecting system 906, and control a patientsupport device such as a treatment couch 975. Digital processing system970 may be configured to register 2D radiographic images received fromdiagnostic imaging system 905, from two or more stereoscopicprojections, with digitally reconstructed radiographs (DRRs) generatedby digital processing system 925 in diagnostic imaging system 905 and/orDRRs generated by processing device 940 in treatment planning system910. Digital processing system 970 may include one or moregeneral-purpose processors (e.g., a microprocessor), special purposeprocessor such as a digital signal processor (DSP) or other type ofdevice such as a controller or field programmable gate array (FPGA).Digital processing system 970 may also include other components (notshown) such as memory, storage devices, network adapters and the like.

In one embodiment, digital processing system 970 includes system memorythat may include a random access memory (RAM), or other dynamic storagedevices, coupled to a processing device, for storing information andinstructions to be executed by the processing device. The system memoryalso may be used for storing temporary variables or other intermediateinformation during execution of instructions by the processing device.The system memory may also include a read only memory (ROM) and/or otherstatic storage device for storing static information and instructionsfor the processing device.

Digital processing system 970 may also include a storage device,representing one or more storage devices (e.g., a magnetic disk drive oroptical disk drive) for storing information and instructions. Thestorage device may be used for storing instructions for performing thetreatment delivery steps discussed herein. Digital processing system 970may be coupled to radiation source 960 and treatment couch 975 by a bus992 or other type of control and communication interface.

Digital processing system 970 may implement methods (e.g., such asmethods 300 through 800 described above) to manage timing of diagnosticx-ray imaging in order to maintain alignment of a target with aradiation treatment beam delivered by the radiation source 960.

In one embodiment, the treatment delivery system 915 includes an inputdevice 978 and a display 977 connected with digital processing system970 via bus 992. The display 977 can show trend data that identifies arate of target movement (e.g., a rate of movement of a target volumethat is under treatment). The display can also show a current radiationexposure of a patient and a projected radiation exposure for thepatient. The input device 978 can enable a clinician to adjustparameters of a treatment delivery plan during treatment. For example,the clinician may select a new image age threshold or target movementthreshold via input device 978.

Treatment planning system 910 includes a processing device 940 togenerate and modify treatment plans. Processing device 940 may representone or more general-purpose processors (e.g., a microprocessor), specialpurpose processor such as a digital signal processor (DSP) or other typeof device such as a controller or field programmable gate array (FPGA).Processing device 940 may be configured to execute instructions forperforming treatment planning operations discussed herein.

Treatment planning system 910 may also include system memory 935 thatmay include a random access memory (RAM), or other dynamic storagedevices, coupled to processing device 940 by bus 986, for storinginformation and instructions to be executed by processing device 940.System memory 935 also may be used for storing temporary variables orother intermediate information during execution of instructions byprocessing device 940. System memory 935 may also include a read onlymemory (ROM) and/or other static storage device coupled to bus 986 forstoring static information and instructions for processing device 940.

Treatment planning system 910 may also include storage device 945,representing one or more storage devices (e.g., a magnetic disk drive oroptical disk drive) coupled to bus 986 for storing information andinstructions. Storage device 945 may be used for storing instructionsfor performing the treatment planning steps discussed herein.

Processing device 940 may also be coupled to a display device 950, suchas a cathode ray tube (CRT) or liquid crystal display (LCD), fordisplaying information (e.g., a 2D or 3D representation of the VOI) tothe user. An input device 955, such as a keyboard, may be coupled toprocessing device 940 for communicating information and/or commandselections to processing device 940. One or more other user inputdevices (e.g., a mouse, a trackball or cursor direction keys) may alsobe used to communicate directional information, to select commands forprocessing device 940 and to control cursor movements on display 950.

Treatment planning system 910 may share its database (e.g., data storedin storage 945) with a treatment delivery system, such as treatmentdelivery system 915, so that it may not be necessary to export from thetreatment planning system prior to treatment delivery. Treatmentplanning system 910 may be linked to treatment delivery system 915 via adata link 990, which may be a direct link, a LAN link or a WAN link.

It should be noted that when data links 983, 984 and 990 are implementedas LAN or WAN connections, any of diagnostic imaging system 905,treatment planning system 910, motion detecting system 906 and/ortreatment delivery system 915 may be in decentralized locations suchthat the systems may be physically remote from each other.Alternatively, any of diagnostic imaging system 905, treatment planningsystem 910, motion detecting system 906 and/or treatment delivery system915 may be integrated with each other in one or more systems.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative embodiments, the methods and apparatus herein may be usedin applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials (e.g., motorblocks in the automotive industry, airframes in the aviation industry,welds in the construction industry and drill cores in the petroleumindustry) and seismic surveying. In such applications, for example,“treatment” may refer generally to the application of radiation beam(s).

It will be apparent from the foregoing description that aspects of thepresent invention may be embodied, at least in part, in software. Thatis, the techniques may be carried out in a computer system or other dataprocessing system in response to its processor, such as digitalprocessing system 970, for example, executing sequences of instructionscontained in a memory. In various embodiments, hardware circuitry may beused in combination with software instructions to implement the presentinvention. Thus, the techniques are not limited to any specificcombination of hardware circuitry and software or to any particularsource for the instructions executed by the data processing system. Inaddition, throughout this description, various functions and operationsmay be described as being performed by or caused by software code tosimplify description. However, those skilled in the art will recognizewhat is meant by such expressions is that the functions result fromexecution of the code by a processor or controller, such as digitalprocessing system 970.

A machine-readable medium can be used to store software and data whichwhen executed by a data processing system causes the system to performvarious methods of the present invention. This executable software anddata may be stored in various places including, for example, systemmemory and storage or any other device that is capable of storingsoftware programs and/or data.

Thus, a machine-readable medium includes any mechanism that provides(i.e., stores and/or transmits) information in a form accessible by amachine (e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine-readable medium includesrecordable/non-recordable media (e.g., read only memory (ROM); randomaccess memory (RAM); magnetic disk storage media; optical storage media;flash memory devices; etc.), as well as electrical, optical, acousticalor other forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.); etc.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative embodiments, the methods and apparatus herein may be usedin applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials. In suchapplications, for example, “treatment” may refer generally to theeffectuation of an operation controlled by the treatment planningsystem, such as the application of a beam (e.g., radiation, acoustic,etc.) and “target” may refer to a non-anatomical object or area.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a computer. The computer-readable medium mayinclude, but is not limited to, magnetic storage medium (e.g., floppydiskette); optical storage medium (e.g., CD-ROM); magneto-opticalstorage medium; read-only memory (ROM); random-access memory (RAM);erasable programmable memory (e.g., EPROM and EEPROM); flash memory; oranother type of medium suitable for storing electronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the communication medium connecting the computer systems.

Although the operations of the methods herein are shown and described ina particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is:
 1. An imaging method, implemented by a computing system programmed to perform the following, comprising: acquiring measurement data indicative of a target motion, wherein the measurement data includes a prior x-ray image; determining, using the computing system, a timing of one or more x-ray images based on the target motion; computing a time to completion of a radiation treatment beam; comparing an age of the prior x-ray image to the time to completion; and when the age of the prior x-ray image will exceed an image age threshold before the time to completion, acquiring a new x-ray image before delivering the radiation treatment beam.
 2. The method of claim 1, further comprising: comparing the prior x-ray image to another image to track the target motion; and visually presenting the target motion via a display.
 3. The method of claim 1, wherein the measurement data includes at least one of ultrasound measurement data or external imaging data of a patient.
 4. An imaging method, implemented by a computing system programmed to perform the following, comprising: acquiring measurement data indicative of a target motion, wherein the measurement data includes a prior x-ray image; determining, using the computing system, a timing of one or more x-ray images based on the target motion; assigning an image age threshold based on the target motion; and establishing an x-ray imaging frequency based on the image age threshold.
 5. The method of claim 4, further comprising: increasing the x-ray imaging frequency when the target motion is above a threshold.
 6. The method of claim 4, further comprising: decreasing the x-ray imaging frequency when the target motion is below a threshold.
 7. The method of claim 4, further comprising: dividing a radiation treatment beam into a plurality of radiation treatment beams, wherein completing delivery of the radiation treatment beam extends beyond the image age threshold.
 8. The method of claim 4, further comprising: combining a plurality of radiation treatment beams into a single radiation treatment beam, wherein delivery of the single radiation treatment beam is complete at or before the image age threshold.
 9. An imaging method, implemented by a computing system programmed to perform the following, comprising: acquiring measurement data indicative of a target motion, wherein the measurement data includes a prior x-ray image; determining, using the computing system, a timing of one or more x-ray images based on the target motion; prior to treatment of a patient, determining a treatment plan that includes a plurality of radiation treatment beams; receiving selection of an initial image age threshold; determining that completing delivery of at least one radiation treatment beam extends beyond the initial image age threshold; and modifying the treatment plan by splitting the at least one radiation treatment beam into two or more radiation treatment beams, wherein delivery of each of the two or more radiation treatment beams will complete at or before the initial image age threshold.
 10. A treatment system, comprising: an imaging apparatus including an x-ray source to generate one or more x-ray images; a motion detecting apparatus to acquire measurement data indicative of a target motion; and a processing device coupled with the imaging apparatus and the motion detecting apparatus, wherein the processing device is configured to: determine a timing of the one or more x-ray images based on the target motion: compute a time to completion of a radiation treatment beam; compare an age of the prior x-ray image to the time to completion; and when the age of the prior x-ray image will exceed an image age threshold before the time to completion, acquiring a new x-ray image before delivering the radiation treatment beam.
 11. The treatment system of claim 10, further comprising: a display; wherein the processing device is further configured to compare the prior x-ray image to another image to track the target motion, and to visually present the target motion via the display.
 12. The treatment system of claim 10, wherein the motion detecting apparatus is an optical tracking system, and wherein the measurement data is generated by at least one of optical tracking of markers disposed on a patient or optical tracking of a surface of the patient.
 13. The treatment system of claim 10, wherein the motion detecting apparatus includes a laser range finder, and wherein the measurement data represents a distance between a surface of the patient and the laser range finder.
 14. A treatment system, comprising: an imaging apparatus including an x-ray source to generate one or more x-ray images; a motion detecting apparatus to acquire measurement data indicative of a target motion; and a processing device coupled with the imaging apparatus and the motion detecting apparatus, wherein the processing device is configured to: determine a timing of the one or more x-ray images based on the target motion; assign an image age threshold based on the target motion; and establish an x-ray imaging frequency based on the image age threshold.
 15. The treatment system of claim 14, wherein the processing device is further configured to increase the x-ray imaging frequency when the target motion is above a threshold.
 16. The treatment system of claim 14, wherein the processing device is further configured to decrease the x-ray imaging frequency when the target motion is below a threshold.
 17. The treatment system of claim 14, wherein the processing device is further configured to divide a radiation treatment beam into a plurality of radiation treatment beams, wherein completing delivery of the radiation treatment beam extends beyond the image age threshold.
 18. The treatment system of claim 14, wherein the processing device is further configured to combine a plurality of radiation treatment beams into a single radiation treatment beam, wherein delivery of the single radiation treatment beam is complete at or before the image age threshold.
 19. The treatment system of claim 14, wherein the motion detecting apparatus is an ultrasound imaging apparatus, and wherein the measurement data is ultrasound measurement data.
 20. A treatment system, comprising: an imaging apparatus including an x-ray source to generate one or more x-ray images; a motion detecting apparatus to acquire measurement data indicative of a target motion; and a processing device coupled with the imaging apparatus and the motion detecting apparatus, wherein the processing device is configured to: determine a timing of the one or more x-ray images based on the target motion; prior to treatment of a patient, determine a treatment plan that includes a plurality of radiation treatment beams; receive selection of an initial image age threshold; determine that completing delivery of at least one radiation treatment beam extends beyond the initial image age threshold; and modify the treatment plan by splitting the at least one radiation treatment beam into two or more radiation treatment beams, wherein delivery of each of the two or more radiation treatment beams is completed at or before the initial image age threshold. 